1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having a fine contact hole with a high aspect ratio, and a method of manufacturing the same.
2. Description of the Prior Art
With micropatterning of a device, the aspect ratio of a contact hole increases. For example, in the case of a 0.35-.mu.m design rule device, if the thickness of an insulating film exceeds 1.5 .mu.m, the aspect ratio becomes 4:1 or more. Even if a barrier metal consisting of Ti/TiN or the like is deposited in such a contact hole having a high aspect ratio, and an Al--Si or Al--Si--Cu alloy is sputtered thereon, a fine contact hole having a high aspect ratio cannot be buried.
For example, one method of burying a fine contact hole having a high aspect ratio by depositing a thin Ge film serving as an underlayer on a barrier metal before sputtering Al--Si or Al--Si--Cu is proposed in Japanese Unexamined Patent Publication No. 4-196421. This method utilizes the phenomena that the eutectic temperature of an Al--Ge alloy formed upon an alloying reaction between Ge and Al in a metal wiring layer is lower than that of Al--Si, and the Al--Ge alloy is easily melted and flows into a fine hole. When an Al--Ge-based alloy is sputtered on a thin Ge film at a temperature lower than that for an Al--Si-based alloy, i.e., at a substrate temperature higher than room temperature and equal to or lower than the eutectic temperature of the Al--Ge-based alloy, the Al--Si-based alloy receives Ge during film formation, and an Al--Ge-Si-based alloy easily flows into a hole due to surface migration.
In addition, for example, another method of burying a contact hole having a high aspect ratio, and at the same time decreasing contact resistance by inserting a Ge layer or an Si layer containing Ge at a high concentration between the bottom portion of the contact hole and an underlying barrier metal is proposed in Japanese Unexamined Patent Publication No. 4-196420.
In these conventional devices, however, the resistance of the wiring layer or electrode varies so as to greatly decrease the reliability of device operation.
FIG. 1 shows contact resistance upon burying a contact hole with Al--5%Ge at once. Note that a polysilicon was used as barrier metal. It is found that the resistance shown in FIG. 1 varies 10% or more.
This is because Ge which has alloyed once and is set in a semi-molten state is precipitated on the barrier metal upon cooling to form a nodule.
To decrease the melting point of the alloy, the content of Ge in the alloy must be increased. As a result, a Ge nodule greatly increases in size because the solution concentration of Ge at room temperature is almost 0.
The presence of such a large Ge nodule in a wiring or electrode metal causes variations in resistance with micropatterning of the contact hole, thereby degrading the electrical characteristics of the device.